Enrichment of Semiconducting Single-Walled Carbon Nanotubes with Indigo-Fluorene-Based Copolymers and Their Use in Printed Thin-Film Transistors and Carbon Dioxide Gas Sensors

Abstract

High-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs) are promising for portable and high-sensitivity gas sensors because of their excellent physical and electrical properties. Here, we describe the synthesis of a novel indigo-fluorene-based copolymer (<b>PFIDBoc</b>) that has been designed to selectively enrich sc-SWCNTs with excellent purity (>99.9%) yet contain a latent function in the form of a <i>tert</i>-butoxy (<i>t</i>-BOC)-protected amine that can be later revealed and exploited for carbon dioxide (CO₂) gas sensing. SWCNTs wrapped with the <b>PFIDBoc</b> polymer can be easily converted via an on-chip thermal process to reveal a vinylogous amide moiety with a secondary amine nitrogen within the indigo building block of the copolymer which is perfectly suited for CO₂ recognition. Thin-film transistors and sensors were inkjet-printed onto rigid and flexible substrates, demonstrating the versatility of enriched <b>PFIDBoc-</b>derived sc-SWCNT dispersions. The printed transistors exhibited a mobility up to 9 cm² V^-1 s^-1 and on/off current ratios >10⁵. We further demonstrate herein a CO₂ sensor for indoor air quality monitoring even in low humidity environments, possessing a linear response with up to ∼5.4% sensitivity and a dynamic range between 400 and 2000 ppm in air with a relative humidity of ∼ 40%.